The present invention relates to an evaporative cooling system for a liquid-cooled internal-combustion engine. More particularly, the invention is directed to a system having a coolant jacket filled completely with coolant, a vapor separator in the forward-flow line to the condenser, a condensate pump arranged in the return flow line from the condenser to the cooling jacket, and a connecting line from the vapor separator parallel to the condenser to the return flow line with an expansion tank connected to the vapor space of the condenser.
From Motortechnische Zeitschrift (MTZ) No. 50 (1989), Volume 9, Page 428, an evaporation cooling system is known which has the advantage that an increased operating temperature may be obtained at partial load but that, at high load, the same efficiency is reached as in a conventional cooling system.
In this known evaporation cooling system which, in a cold condition, is filled only partially with coolant, a closed expansion tank with a variable volume is provided for venting purposes. However, this tank requires additional installation space. Also, additional measures must be provided in order to fill this evaporation cooling system with the coolant.
It is, therefore, an object of the present invention to provide an evaporation cooling system in which additional installation space for an expansion tank is not required.
This object has been achieved in accordance with the present invention by connecting the expansion tank to atmosphere when the coolant is cold and, at the operating temperature of the coolant, disconnecting the expansion tank from the atmosphere. The solution is based on the basic recognition that a connection should be established between the cooling system and the atmosphere as a function of the temperature. In this case, the connection to the atmosphere is maintained until it is ensured that no vapor can escape. If vapor were to escape, this would result in a loss of liquid and thus in a correspondingly increased liquid reserve or a constant refilling of cooling liquid. Both requirements are prevented with the present invention. As a result, even when the hot cooling system cools down and there is therefore a falling below a minimum temperature, the cooling system may again be connected with the atmosphere. This prevents the occurrence of a low pressure in the cooling system.
The present invention further provides a simple way to carry out the venting as a function of the temperature with low equipment expenditures. The thermostatic valve may, for example, be made from a bimetal.
According to another feature of the present invention, air can escape and water is held back. The air exchange proper takes place via a pressure difference between the atmosphere and the cooling system at a molecular sieve.
Yet another feature of the present invention is that simultaneously a filling opening is created which corresponds to the cover in the case of conventional cooling systems operating with cooling liquid as the heat transfer medium. A separate filling opening for the coolant is unnecessary.
It is possible to integrate a pressure control valve in the cover in accordance with the features of the present invention. This creates a connection to the atmosphere which operates as a function of the pressure in addition to the connection operating as a function of the temperature.
A separating system for the liquid coolant is also formed in accordance with the present invention. By virtue thereof, it is ensured that virtually no entrained liquid reaches the vent valve and the molecular sieve.
With the expansion tank of the present invention, it is possible to construct the bottom of the expansion tank as the coolant storage space. A level indicating device that is suitable for this purpose is also provided and can be configured as a float connected with a window plate arranged in the area of the cover.